Title: Deciphering cosmic history and cosmic-ray physics with radio emission

Abstract: Historically, the power of radio astronomy has been focused on exotic objects and high-energy events, largely because the more ubiquitous processes governing galaxy growth and evolution —such as star formation and subsequent supernovae—produce very weak radio sources. Modern radio interferometers can now probe the most fundamental metric of when and how quickly galaxies built up their stellar mass: the evolution of the star formation rate density (SFRD). The peak in the cosmic star formation rate density—at z ~ 2—also marks the peak of dust attenuation, making the full census of star formation activity at short wavelengths a measurement fraught with uncertainty. Fortunately, radio emission from normal galaxies—free-free emission of massive stars, and synchrotron emission of relativistic electrons shocked in the supernovae remnants of massive stars—is entirely unaffected by dust. It is only now that our telescopes have the sensitivity to constrain the star formation activity of populations of normal galaxies like our Milky Way over nearly all cosmic time. My results reveal a discrepancy between measurements of the SFRD at UV+IR wavelengths and at radio frequencies, indicating we may be missing over half of the total star formation, even at redshifts as low as z ~ 0.5. In this talk, I will outline ongoing and future plans to reveal the source(s) of this discrepancy. I will also present recent work on how radio emission from a nearby galaxy is illuminating the roles of cosmic-rays and magnetic fields in the enrichment of the ISM and CGM.